In the Silmarillion, Eol is the name of an elf of Beleriand. He was a famous smith and had a penchant for the darkness. In the Silmarillion, he was an elf of the Teleri, and dwelt on the fringes of Doriath, operating a smithy where he discovered and made unique, powerful weapons.

Those familiar with Tolkien's mythology know that fondness of darkness and obsession with technology are often signs that something bad is going to happen. Such it is with Eol, who married a Noldorin princess, and kept her somewhat unhappily in his darkened woods, and after she tried to escape, ended up killing her, by accident, in a rage. Although there is some history of violence in the elves, especially in the fratricidal period of the War of the Jewels, this is the only recorded story we have of an elf killing a spouse or other close family member.

After his wife-to-be, Aredhel, got tired of the hidden city of Gondolin, she found her way to his woods. They married, and later produced one child, Maeglin. Maeglin took after his father in many ways, but still accompanied his mother when she decided to go back to Gondolin, having grown tired of the dark, furtive existence in Eol's woods. Eol follows them, and is captured trying to enter Gondolin. Since Gondolin was a hidden realm, he was forbidden to leave, and tried to kill his son in a rage at his captivity. He ended up killing his wife instead and was thrown to his death. An ending that to "all in Gondolin it seemed just". My description here doesn't do justice to the story. It should be noted, that in true Silmarillion style, the death doesn't end here, but continues to haunt the works, leading to the eventual destruction of Gondolin.

I have been reading Tolkien since I was six years old, and each time I read the works, I learn something new. The most recent thing I learned was that Tolkien does not always believe the words he puts into the mouths of his characters. Eol is, as far as I know from Tolkien's works, the only elf ever killed by capital punishment. To the people of Gondolin, this seems just. I think, however, that Eol's death sentence is seen as a bad judgement on the part of Turgon, king of Gondolin. On the level of common sense, Eol was trying to strike down his son in a moment of rage, not planning a premeditated murder. Even by our human standards, his crime seems closer to manslaughter than to murder. The elves would seem to be held to a higher standard of wisdom and compassion, and yet they kill him with seemingly no second thoughts. It is also somewhat ironic that the crime that Eol is condemned for, murdering a family member, is paralleled by the fact that the Noldorin elves on a whole were responsible for murdering their cousins in the Kinslaying, and were being punished for it by being exiled.

While Eol is portrayed as being a strange, furtive, somewhat sinister elf, and his crime of killing his wife was certainly a very violent act, even for the time; he was condemned to death for a premeditated murder, an act that Tolkien is perhaps suggesting was unjust, and he was perhaps portraying it as one more act of violence and revenge that eventually caught Gondolin in its web and carried it down into ruin.